I know I'm talking to the wrong side of the wall, but I'm sure there's someone among you collecting "even" TI calculators.

I received for free a basic TI-2550 III which looks new, complete with box, leather pouch and manual (or booklet, I'd say); since it lacks the battery pack, I suppose it was cannibalized in past years. If so, the probability it's broken is very high, nonetheless I'd want to see if it works.

Do you know if and where TI BP3 battery packs are still sold? On the Datamath Calculators Museum there's no evidence of this.

Texas Instruments does not sell these battery packs anymore. If you can't find one on ebay, here may be the next best thing. This suggestion primarily hinges on one thing; is the BP1A battery pack of the same physical size and shape as the BP3? From the photos at datamath.org, it looks possible. It is possible to purchase new BP-1As, from ebay, and directly from a company based in Dallas. If the physical sizes are the same, it would not be too difficult to open up a BP-1A, remove two of the ni-cads, rewire the remaining Ni-Cad to the contact terminals, and glue it back together. Confirming polarity would be necessary.

Here is another possibility. My inventory notes that one of my 2550III's has a nine volt connector soldered to the battery pack connector. I can't tell you about polarity at this time. I expect to go to my winter home in a week or so. I can look at the unit then and tell you what I see.

The idea of wiring in a nine volt connector is similar in concept to what users did with the TI-55. It used nine volts generated by a battery pack, but the connector was different. There were several battery packs of that general design -- the BP-7 and BP-8, for example. They used two NiCad AA cells and a circuit board to convert the output from the cells to a nine volt output. Finding one that works is not so easy these days. If the cells leak the circuit board was typically damaged beyond repair.

To solve my problem (surpassing it) I asked the people who gave me the calculator if they had the AC/DC charger: they did. I tried, but the calculator goes on showing all the blue digits lighting on and off, like they were running on the display. Typing keys shows some effect of the segments (so I assume they work) but the running doesn't stop.

The result is, I guess: BROKEN! Any ideas about the way to fix it?

-- Antonio

P.S.
I'm going on holidays, this evening (Friday 18.30, Central Europe Time), and for a week I won't be able to read your posts. So don't think I'm not grateful.

In many of these old TI calculators, the battery was required to act as a voltage regulator, as there was not a separate one built into the calculator. Essentially, the calculator was not designed to run off the adaptor without the battery installed. Many of the manuals state this. They also state the calculator may be damaged by trying to use the calculator with the charger and without a battery. It's possible that your calculator is bad, or it may still be good, but just acted erratically because of the unregulated voltage.